Use an affine formula to mix stats and eval

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index b34d4ae7c108abfb2040a1dac2eb2da8bff632e1..3d9c718b9df304c77c37885af263adb9f9b95727 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -584,7 +584,8 @@ namespace {
         if (   Threads.stop.load(std::memory_order_relaxed)
             || pos.is_draw(ss->ply)
             || ss->ply >= MAX_PLY)
-            return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) : VALUE_DRAW;
+            return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) - 10 * ((ss-1)->statScore > 0)
+                                                    : VALUE_DRAW;
 
         // Step 3. Mate distance pruning. Even if we mate at the next move our score
         // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
@@ -712,7 +713,7 @@ namespace {
     {
         // Never assume anything on values stored in TT
         if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
-            eval = ss->staticEval = evaluate(pos);
+            eval = ss->staticEval = evaluate(pos) - 10 * ((ss-1)->statScore > 0);
 
         // Can ttValue be used as a better position evaluation?
         if (    ttValue != VALUE_NONE
@@ -721,12 +722,14 @@ namespace {
     }
     else
     {
-        ss->staticEval = eval =
-        (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
-                                         : -(ss-1)->staticEval + 2 * Eval::Tempo;
+        int p = (ss-1)->statScore;
+        int malus = p > 0 ? (p + 5000) / 1024 :
+                    p < 0 ? (p - 5000) / 1024 : 0;
 
-        tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
-                  ss->staticEval);
+        ss->staticEval = eval = (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) - malus
+                                                                 : -(ss-1)->staticEval + 2 * Eval::Tempo;
+
+        tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
     }
 
     // Step 7. Razoring (~2 Elo)